1. Field of the Invention
The present invention relates to a tool designed to drill holes in concrete and other materials.
2. Description of the Prior Art
Holes have been drilled in concrete using masonry drill bits for many years. One problem that has persisted, especially when relatively large-diameter holes are drilled into concrete using a cylindrical, annular core drill bit, is that it is sometimes difficult to maintain the drill bit precisely centered so as to drill a completely circular and aligned large diameter hole into concrete, fiberglass, plastic, and other materials. The problem arises due to the tendency for one edge of the drill to make contact before another edge. Consequently, the drill tries to walk sideways erratically. There is a tendency for the drill bit to wobble or vibrate in a lateral direction, rather than stay precisely centered on the intended drill bit axis. As a result, it is difficult to drill holes in concrete, particularly large diameter holes, with portable equipment.
One prior system that has been developed to attempt to stabilize a drill bit is available under the trade designation “Core Drill Rig”. This device operates somewhat in the manner of a drill press. However, unlike a drill press, there can be no stabilizing table beneath a workpiece when drilling into concrete. This is because the concrete structure into which a hole is drilled is always much too thick and expansive to lend itself to stabilization by a table located beneath the drill.
The Core Drill Rig employs a relatively large diameter, annular drill bit mounted on a drill held by a stanchion to one side of a frame. It is necessary to bolt the frame of the Core Drill Rig to the concrete surface to be drilled or hold it in place by suction in order to provide resistance to the drill bit so that the drill bit can penetrate the concrete. If the drill supporting frame is not bolted or otherwise secured to the concrete floor, the drill bit tends to lift off the concrete surface being drilled.
The supporting frame is provided with bolt holes and bolts that must be attached to the concrete structure into which the relatively large diameter hole is to be drilled. First, relatively small diameter holes must be drilled in the concrete at the bolt locations to allow the Core Drill Rig frame to be secured to a concrete floor or wall into which a large diameter hole is to be drilled. Once the frame is bolted to the surface it provides the drill bit with much greater stability than can be achieved using a hand-held drill. However, since the Core Drill Rig must be bolted to the surface, the holes that are used to attach the bolts that secure the frame to the concrete surface must later be filled. Also, considerable effort is required to bolt the frame to the surface to be drilled.
The Core Drill Rig can be configured with a vacuum device that creates a suction to draw the drill frame down to the concrete floor. However, it is difficult to achieve a sufficient suction force to prevent the frame from lifting off the floor and breaking the vacuum if one attempts to operate the drill with high torque. To the contrary, in conventional systems such as the Core Drill Rig, the large diameter drill bit can only be operated at a relatively low speed with a high torque in order for the hole drilled to be circular within acceptable tolerances.
Furthermore, conventional concrete core drills that employ stabilizing frames, such as the Core Drill Rig, are very bulky, heavy, and expensive. They cannot be conveniently packed in a small carry case. They also require a considerable volume of space for transportation in a truck or other work vehicle.
Another conventional annular drilling arrangement is the common hole saw. This is used primarily for cutting holes in wood. The hole saw incorporates a pilot drill fixed in the center of an annular strip of saw blade. The drill bit is simply attached to a chuck driven by a hand drill motor and the pilot drill makes a smaller hole to start off with. As the depth of drilling process progresses the larger annular drill bit engages. At this time the smaller hole acts as a guide for the larger drill.
Although this drilling system has been around for many years it is unsatisfactory for many materials, including concrete. The desirable features of the cutting action for the smaller pilot bit are not the same as those for the cutting action of the larger hole saw. For substances like concrete a percussion action is ideal for drills up to approximately one inch in diameter using carbide tips shaped to pulverize their way through the material with the percussion action. This action is not practical for the larger diameter, thin walled core bit that a hand held drill motor can practically hammer and rotate. Similarly a high rotational speed is more suited to the small pilot drill bit but these speeds may exceed the optimum speed for the large core bit, thus causing overheating and failure of the bit or melting of the material to be cut. In addition, the pilot drill is not aligned in an orientation that can be checked for accuracy before commencing the drilling of the larger hole. Also, the guiding tolerance does not remain constant since the pilot drill tends to “oval” the pilot hole with continued rotation thus causing irregular holes, variable location and misalignment.